In theory, a new magnetron in the same model of a microwave oven should not cook differently from an old one, assuming that both magnetrons are functioning properly and have the same specifications. The magnetron is the component responsible for generating the microwave radiation used for cooking food in a microwave oven. As long as the new magnetron has the same power output and specifications as the old one, it should produce similar cooking results.
However, in practice, there might be some variations in magnetron performance due to manufacturing tolerances or other factors. Additionally, over time, the efficiency of a magnetron can degrade, which might lead to slightly different cooking results compared to a brand new one in the same model.
If you're experiencing significant differences in cooking performance after replacing the magnetron in your microwave oven, it's possible that there could be other issues affecting the microwave's functionality or that the new magnetron has a different power output or specifications than the original one. In such cases, it's best to consult the manufacturer or a qualified technician to ensure the microwave is operating correctly and safely.